Dr. Christine Johnston completed Infectious Diseases fellowship and an MPH degree in epidemiology at the University of Washington in 2007. This proposal describes a 5 year training program which will allow her to develop an independent academic career in clinical research studying genital herpes simplex virus-2 (HSV-2) infection, and will build on prior experiences studying host-viral interactions and herpesvirus replication at mucosal surfaces. Drs. Anna Wald and Lawrence Corey are internationally renowned leaders in clinical HSV-2 research and are co-mentors for this award. HSV-2 is the most prevalent sexually transmitted infection worldwide and has emerged as a significant risk factor for acquisition and transmission of HIV. HSV-2 transmission most frequently occurs during periods of asymptomatic genital shedding. Our group has recently used intensive sampling (swabbing the genital surfaces 4 times per day) to demonstrate that the majority of genital shedding episodes last less than 12 hours, suggesting a frequent reactivation rate from the ganglia and a brisk peripheral immune response. Preliminary data indicate that subclinical shedding may occur simultaneously at several genital locations and that "short bursts" of HSV-2 replication occur in the presence of suppressive antiviral therapy. These data suggest that 1) we may have overestimated the degree of suppression provided by antiviral therapy and 2) genital mucosal responses are essential for control of HSV-2 replication. To evaluate "short bursts" of shedding, a cohort of 50 HSV-2 seropositive persons on suppressive antiviral therapy will obtain genital swabs 4 times per day for 60 days. The rate and duration of HSV-2 shedding episodes will be compared with rates off therapy (Aim 1). For Aims 2 &3,15 HSV-2 seropositive people not on therapy (Aim 2) and 15 persons on suppressive therapy (Aim 3) will be seen daily over a 30 day period to capture episodes of asymptomatic shedding, using a novel rapid HSV PCR test. Genital biopsies will be performed within hours of HSV-2 detection. Gene expression patterns using microarrays and HSV specific T-cell function will be evaluated. Results will be compared to biopsies obtained from the same participants in the presence of genital lesions. These studies will help us understand HSV-2 pathogenesis and the responses mediating viral clearance, which will inform therapeutic strategies to prevent the epidemic spread of HSV-2 and HIV.